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Inheritance Runway Calculator

Calculate when a windfall inheritance will go bankrupt against inflation, returns, and monthly lifestyle extractions.

Note: This is a static amortization model. It assumes a fixed, guaranteed return. Real-world market volatility (Sequence of Returns Risk) and inflation will heavily impact these results.

The Capital Base

$

The net windfall amount deposited into your investment/savings account.

Withdrawal Mechanics

$/ mo
%
%

Capital Depletion Schedule

Annual snapshots showing the progressive collapse of the principal balance over time based on your 5% Expected Annual Return input above.

TimelineStart BalanceStatic WithdrawalReal Value (2.5% Inflation)Interest (5%)End Balance
Year 1Month 1
$500,000-$2,500$2,495+$2,027$499,527
Year 1Month 12
$494,688-$2,500$2,439+$2,005$494,194
Year 2Month 24
$488,616-$2,500$2,380+$1,980$488,097
Year 3Month 36
$482,241-$2,500$2,321+$1,955$481,695
Year 4Month 48
$475,546-$2,500$2,265+$1,927$474,974
Year 5Month 60
$468,517-$2,500$2,210+$1,899$467,916
Year 6Month 72
$461,137-$2,500$2,156+$1,869$460,505
Year 7Month 84
$453,387-$2,500$2,103+$1,837$452,724
Year 8Month 96
$445,250-$2,500$2,052+$1,804$444,554
Year 9Month 108
$436,706-$2,500$2,002+$1,769$435,975
Year 10Month 120
$427,735-$2,500$1,953+$1,732$426,967
Year 11Month 132
$418,315-$2,500$1,905+$1,694$417,509
Year 12Month 144
$408,424-$2,500$1,859+$1,654$407,578
Year 13Month 156
$398,039-$2,500$1,814+$1,611$397,151
Year 14Month 168
$387,135-$2,500$1,769+$1,567$386,202
Year 15Month 180
$375,685-$2,500$1,726+$1,520$374,705
Year 16Month 192
$363,663-$2,500$1,684+$1,471$362,634
Year 17Month 204
$351,039-$2,500$1,643+$1,420$349,959
Year 18Month 216
$337,785-$2,500$1,603+$1,366$336,651
Year 19Month 228
$323,868-$2,500$1,564+$1,309$322,677
Year 20Month 240
$309,255-$2,500$1,526+$1,250$308,004
Year 21Month 252
$293,911-$2,500$1,488+$1,187$292,598
Year 22Month 264
$277,800-$2,500$1,452+$1,122$276,422
Year 23Month 276
$260,884-$2,500$1,417+$1,053$259,436
Year 24Month 288
$243,121-$2,500$1,382+$980$241,602
Year 25Month 300
$224,471-$2,500$1,348+$904$222,875
Year 26Month 312
$204,888-$2,500$1,316+$825$203,213
Year 27Month 324
$184,326-$2,500$1,283+$741$182,567
Year 28Month 336
$162,736-$2,500$1,252+$653$160,889
Year 29Month 348
$140,066-$2,500$1,222+$560$138,127
Year 30Month 360
$116,263-$2,500$1,192+$463$114,227
Year 31Month 372
$91,270-$2,500$1,163+$362$89,131
Year 32Month 384
$65,027-$2,500$1,134+$255$62,782
Year 33Month 396
$37,472-$2,500$1,107+$142$35,114
Year 34Month 408
$8,539-$2,500$1,080+$25$6,063
FINAL MONTHMonth 411
$1,082-$1,082$1,073+$0$0

Fund Depletion Risk: The principal will run out

Inheritance Runway

34 Yrs, 3 Mos
Until the account hits $0
Monthly Cash Flow Equation:
Interest Generated in Month 1:+$2,037
Monthly Lifestyle Extraction:-$2,500
Net Trajectory:Depleting

You are pulling out $463 more than the money generates organically every month. You are actively destroying your principal base.

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What is The Math of Windfall Depletion?

A sudden, massive injection of capital (an inheritance, the sale of a business, winning the lottery) tricks the human brain. $500,000 feels like 'impossible to spend' money. But if you park it in an account and pull out $4,000 a month to live a slightly elevated lifestyle, the compounding math of sequential withdrawals works violently against you, driving the balance to absolute zero much faster than intuition suggests.

Mathematical Foundation

N=−ln⁡(1−(PV×i/PMT))ln⁡(1+i)N = \frac{-\ln(1 - (PV \times i / PMT))}{\ln(1 + i)}
PVPV= Present Value (The Lump Sum inheritance base).
PMTPMT= Payment (The monthly withdrawal you take out).
ii= The monthly interest rate (Annual Rate / 12).
NN= The exact number of months until the account goes bankrupt.

Laws & Principles

  • The Equilibrium Trap: If your monthly withdrawal exactly equals the monthly interest generated by the principal, the money lasts forever. But if you withdraw even $100 MORE than the interest generated, you start shrinking the principal. A smaller principal generates less interest next month, so the $100 shortfall becomes a $105 shortfall, accelerating exponential portfolio death.
  • Inflation Erosion: This model calculates mathematical zero. It does not account for housing/food inflation. $2,500/mo buys a lot less in year 15 than it does in year 1. To be truly safe, your withdrawal rate should be significantly lower than the yield to allow the principal to grow with inflation.
  • Sequence of Returns Risk: We assume a flat, guaranteed return. In the real stock market, withdrawing fixed cash during a brutal negative-return bear market permanently destroys shares, drastically shortening the runway.

Step-by-Step Example Walkthrough

" A 40-year-old inherits $500,000. They invest it in a conservative portfolio yielding 5% annually, and decide to quit their job and withdraw $2,500 every month. "

  1. Monthly Yield: At 5% APR, the $500,000 generates roughly $2,083 in interest the first month.
  2. The Shortfall: They withdraw $2,500. $2,083 comes from interest, and the remaining $417 is sold out of the $500k principal.
  3. The Spiral: Month 2 starts with a principal of $499,583. It generates slightly less interest. The $2,500 withdrawal eats a slightly larger chunk of the principal.
Final Result: The money lasts exactly 34 years and 3 months. It evaporates when they are 74 years old, leaving them with zero capital right as their medical expenses are statistically peaking.

Quick Answer: How does the Inheritance Runway Calculator work?

This tool calculates the precise duration a lump sum of money will last when subjected to fixed monthly withdrawals and estimated investment returns. You input your total inherited windfall, how aggressively you plan to invest it (Expected Return), and your desired monthly lifestyle budget. The calculator simulates the depletion curve over time, factoring in the erosion of capital, to tell you exactly how many years and months remain until the account hits zero.

The Windfall Depletion Formula

Amortization of Capital

Next Month Balance = (Current Balance + Interest Earned) − Monthly Withdrawal

When the Monthly Withdrawal exceeds the Interest Earned, the principal shrinks. This causes future interest to shrink, creating an accelerating downward spiral toward zero.

Wealth Scenarios

✓ The Perpetual Trust Strategy

Living entirely off the yield without touching the principal.

  1. Lump Sum Inherited: $1,000,000.
  2. Expected Annual Return: 6% ($60,000/year or $5,000/mo).
  3. Monthly Withdrawal: $4,000/mo.
  4. Result: The portfolio generates $1,000 more a month than is being spent.

→ Infinite Runway. The principal actually grows over time, protecting against inflation while funding a $48k/year lifestyle forever.

✗ The Lifestyle Creep Collapse

Upgrading lifestyle expecting the windfall to last forever.

  1. Lump Sum Inherited: $300,000.
  2. Expected Annual Return: 4% ($1,000/mo interest).
  3. Monthly Withdrawal: $3,500/mo (New car lease, upgraded apartment).
  4. Principal Burn: Removing $2,500 of core capital every single month.

→ Complete Bankruptcy in 8 Years. The entire $300,000 inheritance is evaporated before the individual reaches their primary retirement years.

The 4% Rule Danger Zones

Monthly Withdrawal 5% Return Runway Outcome
$1,500/mo (3.6%) Infinite Growth
$2,000/mo (4.8%) 54 Years Stable
$2,500/mo (6.0%) 34 Years Depleting
$3,500/mo (8.4%) 18 Years High Risk
$5,000/mo (12.0%) 10 Years Rapid Collapse

Maximizing Inheritance Lifespan

Do This

  • ✓Implement the 6-Month Pause. When receiving over $100k, park it in a High Yield Savings Account (HYSA) or Treasury Bills for 6 months. Do not quit your job, buy a car, or pay off friends' debts. Let the psychological heat fade before deploying the capital into equities.
  • ✓Cap withdrawals below 4%. If you intend for the money to last your entire life, your maximum annual withdrawal should never exceed 3.5% to 4.0% of the initial balance. This leaves enough remaining growth to cushion against inflation.

Avoid This

  • ✗Beware Sequence of Returns Risk. Pulling heavy withdrawals during a stock market crash (like 2008 or 2022) forces you to sell assets at a massive discount. This permanently destroys the capital base and can slice your runway in half.
  • ✗Don't ignore inflation friction. A $3,000 monthly withdrawal may feel luxurious today, but with 3% annual inflation, you will need nearly $6,000/month in 24 years just to maintain the exact same purchasing power.

Frequently Asked Questions

Should I pay off my mortgage with an inheritance?

It depends on your interest rate. If you have a legacy 3% mortgage, mathematically it is better to keep the mortgage and invest the inheritance in equities yielding 7-9%. However, if you have a 7% or 8% mortgage, paying it off offers a guaranteed, risk-free 8% return on that capital, which is incredibly powerful.

Do I owe taxes on an inherited lump sum?

Usually no, at least at the federal level. Cash inheritances and life insurance payouts are generally federal income tax-free to the beneficiary. However, if you inherit a traditional IRA or 401(k), you will owe income taxes on withdrawals. Six US states also charge a separate inheritance tax.

What does "Infinite Runway" mean?

An infinite runway occurs when your monthly withdrawal is less than or equal to the interest the portfolio generates. Because you never actually touch the principal base, the account never depletes (assuming constant returns).

Why does the capital deplete so fast at the end?

This is reverse compounding. As your balance drops, it generates less interest the following month. But your lifestyle withdrawal stays the same. Therefore, a larger percentage of your withdrawal must be pulled from the core principal every single month, accelerating the collapse.

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